#!/usr/bin/env python3
# Tcp Port Forwarding (Reverse Proxy)
# Author : WangYihang <wangyihanger@gmail.com>

"""
+-----------------------------+         +---------------------------------------------+         +--------------------------------+
|     My Laptop (Alice)       |         |            Intermediary Server (Bob)        |         |    Internal Server (Carol)     |
+-----------------------------+         +----------------------+----------------------+         +--------------------------------+
| $ ssh -p 1022 carol@1.2.3.4 |<------->|    IF 1: 1.2.3.4     |  IF 2: 192.168.1.1   |<------->|       IF 1: 192.168.1.2        |
| carol@1.2.3.4's password:   |         +----------------------+----------------------+         +--------------------------------+
| carol@hostname:~$ whoami    |         | $ python pf.py --listen-host 1.2.3.4 \      |         | 192.168.1.2:22(OpenSSH Server) |
| carol                       |         |                --listen-port 1022 \         |         +--------------------------------+
+-----------------------------+         |                --connect-host 192.168.1.2 \ |
                                        |                --connect-port 22            |
                                        +---------------------------------------------+
"""

import socket
import threading
import argparse
import logging

format = "%(levelname)s: %(message)s"
logging.basicConfig(level=logging.DEBUG, format=format)


def handle(buffer, src_address, src_port, dst_address, dst_port):
    """
    intercept the data flows between local port and the target port
    """
    logging.debug(
        f"{src_address, src_port} -> {dst_address, dst_port} {len(buffer)} bytes"
    )
    logging.debug(f"{buffer}\n")
    # if b"\xbc\xb1\xe6\x57" in buffer:
    #     return buffer + b"A" * 64
    return buffer


def transfer(src, dst):
    src_address, src_port = src.getsockname()
    dst_address, dst_port = dst.getsockname()
    while True:
        try:
            buffer = src.recv(4096)
            if len(buffer) == 0:
                break
            dst.send(handle(buffer, src_address, src_port, dst_address, dst_port))
        except Exception as e:
            logging.error(repr(e))
            break
    logging.warning(f"Closing connect {src_address, src_port}! ")
    src.close()
    logging.warning(f"Closing connect {dst_address, dst_port}! ")
    dst.close()


def server(local_host, local_port, remote_host, remote_port):
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server_socket.bind((local_host, local_port))
    server_socket.listen(0x40)
    logging.info(f"Server started {local_host, local_port}")
    logging.info(
        f"Connect to {local_host, local_port} to get the content of {remote_host, remote_port}"
    )
    while True:
        src_socket, src_address = server_socket.accept()
        logging.info(
            f"[Establishing] {src_address} -> {local_host, local_port} -> ? -> {remote_host, remote_port}"
        )
        try:
            dst_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            dst_socket.connect((remote_host, remote_port))
            logging.info(
                f"[OK] {src_address} -> {local_host, local_port} -> {dst_socket.getsockname()} -> {remote_host, remote_port}"
            )
            s = threading.Thread(target=transfer, args=(dst_socket, src_socket))
            r = threading.Thread(target=transfer, args=(src_socket, dst_socket))
            s.start()
            r.start()
        except Exception as e:
            logging.error(repr(e))


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--listen-host", help="the host to listen", required=True)
    parser.add_argument(
        "--listen-port", type=int, help="the port to bind", required=True
    )
    parser.add_argument(
        "--connect-host", help="the target host to connect", required=True
    )
    parser.add_argument(
        "--connect-port", type=int, help="the target port to connect", required=True
    )
    args = parser.parse_args()
    server(args.listen_host, args.listen_port, args.connect_host, args.connect_port)


if __name__ == "__main__":
    main()